This application claims priority of International Application PCT/IB99/01220 filed Jun. 30, 1999 with priority of RU 98113117 filed Jul. 3, 1998.
The invention pertains to the field of jet technology, primarily to pump-ejector units for evacuation and compression of various gaseous mediums.
An operating process of a pump-ejector system is known, which consists in the delivery of a liquid medium into nozzles of first-stage and second-stage liquid-gas ejectors by a pump, evacuation of a gaseous medium by the first-stage ejector, discharge of a gas-liquid mixture containing the evacuated gaseous medium from the first-stage ejector into a first-stage gravity-inertial separator, evacuation of a gaseous medium from the first-stage separator by the second-stage ejector and discharge of a gas-liquid mixture from the second-stage ejector into a second-stage separator (see patent, RU, 2094070, 27.10.97).
The same patent also introduces a multiple-stage pump-ejector system having a first-stage liquid-gas ejector, a second-stage liquid-gas ejector, a first-stage gravity-inertial separator, a second-stage separator and a pump intended for delivery of a liquid medium from the second-stage separator into nozzles of the first-stage and second-stage ejectors.
The described operational process and the system for its embodiment provide evacuation of a gaseous medium from a vacuum rectification column and consequently a vacuum in the column. However such process and system do not allow sequential compression of the evacuated gas stage by stage. Therefore the application ranges of the process and the system are limited.
The closest analogue of the operational process introduced by the present invention is an operational process of a pump-ejector unit, which includes delivery of a motive liquid into nozzles of first-stage and second-stage liquid-gas ejectors by a pump, evacuating a gaseous medium by the first-stage ejector, compressing the gaseous medium in the first-stage ejector, discharging a gas-liquid mixture containing the evacuated gaseous medium from the first-stage ejector into a first-stage separator, separating the mixture in the first-stage separator into compressed gas and motive liquid, evacuating the compressed gas from the first-stage separator by the second-stage ejector, additionally compressing the evacuated compressed gas in the second-stage ejector, discharging a gas-liquid mixture containing the additionally compressed gas from the second-stage ejector into a second-stage separator, separation of the mixture in the second-stage separator into the additionally compressed gas and the motive liquid and subsequent delivery of the additionally compressed gas from the separator to consumers, and bypassing the motive liquid from the first-stage separators into the second-stage one (see application WO 96/16711, published on Jun. 6, 1996).
The same application describes a pump ejector unit having a first-stage ejector and a first-stage separator, a second-stage ejector and a second-stage separator, and a pump. A discharge side of the pump is connected to the nozzles of the first-stage and second-stage ejectors, the gas inlet of the first-stage ejector is connected to a source of an evacuated gaseous medium, an outlet of the first-stage ejector is connected to the first-stage separator, the gas inlet of the second stage ejector is connected to the gas outlet of the first-stage separator, an outlet of the second-stage ejector is connected to the second-stage separator, and the two separators are interconnected by a pipe.
With this operating process and related pump-ejector unit it is possible to evacuate a gaseous medium from a reservoir, for example from a rectification column. But the introduced layout and design of the system propose feeding a motive liquid from the first-stage separator into the second-stage one and only then delivery of the liquid from the second-stage separator into the ejectors by the pump. As a result, motive liquid with a high content of dissolved gases is fed into the ejectors nozzles. This negatively affects capacity of the ejectors, especially performance of the first-stage ejector intended for maintaining the required pressure in the evacuated reservoir.
This invention is aimed at increasing capacity of a pump-ejector system and at improving operational reliability of the system.
With regard to the operating process as the subject-matter of the invention, the stated technical problem is solved as follows: an operating process of a pump-ejector system, which includes delivery of a liquid medium into the nozzles of first-stage and second-stage liquid-gas ejectors by a pump, evacuating a gaseous medium by the first-stage ejector, compressing the gaseous medium in the first-stage ejector, discharging a gas-liquid mixture containing the evacuated gaseous medium from the first-stage ejector into a first-stage separator, separating the mixture in the first-stage separator into compressed gas and motive liquid, evacuating the compressed gas from the first-stage separator by the second-stage ejector, additionally compressing the evacuated compressed gas in the second-stage ejector, discharging a gas-liquid mixture containing the additionally compressed gas from the second-stage ejector into a second-stage separator, separating the mixture in the second-stage separator into the additionally compressed gas and the motive liquid and subsequent delivery of the additionally compressed gas from the second-stage separator to consumers, where bypassing the motive liquid between the first-stage and second-stage separators is modified so that the motive liquid passes from the second-stage separator into the first-stage separator wherefrom the motive liquid is fed into the nozzles of the first-stage and second-stage ejectors by the pump.
The bypassing of the motive liquid from the second-stage separator into the first-stage one is forced by a difference between pressures in the second-stage and first-stage separators, and the volume of the bypassed motive liquid is adjusted by an artificially created hydraulic resistance. The motive liquid is cooled prior to its delivery to the suction port of the pump.
With regard to the apparatus as the subject-matter of the invention, the mentioned technical problem is solved as follows:
A multiple-stage pump-ejector system, which has a first-stage ejector, a first-stage separator, a second-stage ejector, a second-stage separator and a pump, and wherein the discharge side of the pump is connected to the nozzles of the first-stage and second-stage ejectors, the gas inlet of the first-stage ejector is connected to a source of an evacuated gaseous medium, an outlet of the first-stage ejector is connected to the first-stage separator, the gas inlet of the second-stage ejector is connected to the gas outlet of the first-stage separator, an outlet of the second-stage ejector is connected to the second-stage separator and the two separators are interconnected by a pipe, and further has the following design features: the suction side of the pump is connected to the first-stage separator, the first-stage and second-stage separators are interconnected by a vertical U-tube acting as a hydro seal, where the height of the U-tube above the motive liquid level in the second-stage separator is not less than the height of liquid column created in the U-tube by the motive liquid from the second-stage separator under a pressure difference between the separators.
In addition, the pump-ejector system can be furnished with a third stage. In this case the gas inlet of a third-stage ejector is connected to the second-stage separator, a nozzle of the third-stage ejector is connected to the discharge side of the pump, an outlet of the third-stage ejector is connected to a third-stage separator, the third-stage separator is connected to the first-stage separator through a vertical U-tube.
There is another variant of the multiple-stage pump-ejector system having a first-stage ejector, a first-stage separator, a second-stage ejector, a second-stage separator and a pump, wherein the discharge side of the pump is connected to the nozzles of the first-stage and second-stage ejectors, the gas inlet of the first-stage ejector is connected to a source of an evacuated gaseous medium, an outlet of the first-stage ejector is connected to the first-stage separator, the gas inlet of the second-stage ejector is connected to the gas outlet of the first-stage separator, an outlet of the second-stage ejector is connected to the second-stage separator and the two separators are interconnected by a pipe. In this variant of an embodiment of the invention, the second-stage separator is furnished with a level gage, the suction side of the pump is connected to the first-stage separator, the first-stage and second-stage separators are interconnected by a pipe, which is furnished with a regulator of the motive liquid flow, and the regulator is connected to the level gage.
In this variant the system can also be furnished with a third stage. In this case the gas inlet of a third-stage ejector is connected to the second-stage separator, a nozzle of the third-stage ejector is connected to the discharge side of the pump, an outlet of the third-stage ejector is connected to a third-stage separator, and the third-stage separator is connected to the first-stage separator through a pipe with a flow regulator. The flow regulator is connected to a level gage of the third-stage separator.
Experiments have shown, that the mode of the motive liquid circulation and the regime of feeding the motive liquid from one separator to another exert a significant influence on the capacity of the multiple-stage pump-ejector system. The regime of the motive liquid feeding from one separator to another also affects the operational reliability of the system. Therefore bypassing of the motive liquid from one separator to another with minimal hydraulic losses and minimal usage of additional equipment with moving parts contributes to a higher reliability and a higher capacity of the system. The difference in pressures in the separators allows bypassing of the motive liquid from the second-stage and third-stage separators to the first-stage separator by gravity, i.e. without usage of any pumping equipment. The availability of the vertical U-tubes between the separators prevents the inrush of gases from the second-stage and third-stage separators into the first-stage separator because these U-tubes simultaneously act as hydro seals between the separators.
It was found, that the content of dissolved gases in the motive liquid significantly affects the capacity of the pump-ejector system. The lower the content of dissolved gases in the motive liquid, the deeper the vacuum which can be obtained at the gas inlet of a liquid-gas ejector while required power input remains the same. Bypassing of the motive liquid from the second-stage and third-stage separators into the first-stage separator and subsequent delivery of the motive liquid from the first-stage separator to the suction port of the pump provides a supply of the motive liquid both into the first-stage and second-stage ejectors from a reservoir (namely from the first-stage separator) wherein pressure is minimal. As a rule, pressure in the first-stage separator is lower than atmospheric. This allows more intensive degassing of the motive liquid. So, the motive liquid with a minimal content of dissolved gases can be fed into the ejectors nozzles. Another embodiment of the multiple-stage system proposes to deliver the motive liquid from the second-stage and third-stage separators into the first-stage separator through the tubes, which are equipped with flow regulators (valve devices for example). Throughput of these regulators depends on the motive liquid level in the second-stage and third-stage separators because the regulators are connected to the level gages of the separators. Subject to the motive liquid level, the level gages transmit appropriate signals to the regulators, so that the regulators open their flow areas when the motive liquid levels in the separators rise.
Thus, the introduced operational process and related multiple-stage system provide a solution to the stated technical problem, i.e. the described multiplestage system implementing the introduced process exhibits an increased reliability and capacity.